• 한국항공우주학회지
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• 제34권10호
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• pp.32-39
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• 2006

노즐 조립체에 대한 구조건전성을 평가하기 위한 구조강도시험에 음향방출 기법을 적용하였다. 이들 결과는 스트레인 및 변위 측정 결과와 비교 분석 되었으며, AE 기법의 신뢰도를 향상시키기 위하여 X-ray를 이용한 NDT 기법이 각 시험 전과 후에 실시되었다. 노즐 조립체에 대한 구조건전성 평가 시험에서 스트레인 및 변위 결과로는 구조물의 국부적인 균열 생성 현상을 정확하게 규명하기 곤란하였으나, AE 기법을 이용함으로써 균열들의 생성위치 및 하중을 정확하게 평가할 수 있었다. 이 시험을 통하여, 사출판과 노즐 조립체 사이에 존재한 간섭현상으로 인한 예기치 않은 하중에서 노즐 조립체의 복합재 내에 새로운 균열이 생성될 수 있음이 확인되었으며, 이들 균열은 구조물의 급격한 기능 상실의 원인이 될 수 있는 것으로 파악되었다.

• 대한기계학회논문집A
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• 제30권4호
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• pp.420-427
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• 2006

The structural and leakage integrity of steam generator tubes should be sustained against all postulated loads even if a crack is present. During the past three decades, most of the efforts with respect to integrity evaluation of steam generator tubes have been focused on limit load solutions but, recently, the applicability of elastic-plastic fracture mechanics was examined cautiously due to its effectiveness. The purpose of this paper is to introduce a testing method to estimate fracture resistance characteristics of steam generator tubes with a through-wall crack. Due to limited thickness and diameter, inevitably, the steam generator tubes themselves were tested instead of standard specimen or alternative ones. Also, a series of three dimensional elastic-plastic finite element analyses were carried out to derive closed-form estimation equations with respect to J-integral and crack extension for direct current potential drop method. Since the effectiveness of $J_{IC}$ as well as J-R curves was proven through comparison with those of standard specimens taken from pipes, it is believed that the proposed scheme can be utilized as an efficient tool for integrity evaluation of cracked steam generator tubes.

• 한국안전학회지
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• 제18권1호
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• pp.8-13
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• 2003

This study proposes integrity evaluation method of weld zone in rails using high precision distance amplitude characteristics curve(DACC) and ultrasonic signals. For these purposes, the ultrasonic signals for defects(porosity and crack) of weld zone in rails are acquired in the type of time series data and echo strength. 6 lines in the DACC indicated damage evaluation standard of weld zone in rails. The aquired ultrasonic signals agree fairly well with the mesured results of reference block and sensitivity block(defect location, beam propagation distance, echo strength, etc). The proposed high precision DACC in this study can be used for integrity evaluation of weld zone in rails.

• 한국철도학회논문집
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• 제5권2호
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• pp.55-60
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• 2002

This study proposes the post-processor simulator construction of ultrasonic signal for integrity evaluation of railway truck. For these purposes, the ultrasonic signals for defects(crack) of weld zone in frames are acquired in the type of time series data and echo strength. The detection of the natural defects in railway truck is performed using the characteristics of echodynamic pattern in ultrasonic signal. The constructed post-processor simulator agree fairly well with the measured results of test block(defect location, beam propagation distance, echo strength, etc). Proposed post-processor simulator construction of ultrasonic in this study can be used for the integrity evaluation of railway truck.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.54-59
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• 2004

In this paper probabilistic fracture mechanics(PFM) approach is employed to evaluate the integrity of CANDU Zr-2.5Nb pressure tubes. Modified failure assessment diagram(Jr-FAD), plastic collapse, and critical crack length(CCL) approach are used for evaluating failure probability of the tubes. Jr-FAD was extended from the Kr-FAD because fracture of pressure tubes occurs in brittle manner due to hydrogen embrittlement of material by deuterium fluence. For developing the probabilistic integrity evaluation module, AECL procedures and fracture toughness parameters of EPRI were used.

• 한국안전학회지
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• 제8권1호
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• pp.13-20
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• 1993

It is well known that mechanisms of fracture and fatigue crack propagation depend upon various characteristics such as environmental condition. crack geometry. heat treatment and mechanical properties. It seems to be important for the detailed evaluation of structural integrity to investigate the effects of the above factors on the behavior of structural components which contain flaws. In this paper. it is studied that the fatigue crack propagation of partly heat treated medium carbon steel (SM45C) by high frequency heat treatment.

• 대한기계학회논문집A
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• 제21권7호
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• pp.1089-1096
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• 1997

In this paper, Rancho Seco transient which is reported as a typical pressurized thermal shock event is postulated to be occuring in the Kori unit 1 plant, the oldest nuclear power plant in Korea. For the given material properties, transient history such as temperature and pressure, and postulated flaw, the stress distribution is obtained to calculate stress intensities for a wide range of assumed crack sizes. The stress intensities are compared with the fracture toughness, which is determined using the material properties and the distribution of the nil ductility transition temperature, to determine if cracking is expected to occur during the transient. The allowable operating year for the transient is determined and the evaluation results are discussed.

• 전산구조공학
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• 제9권2호
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• pp.153-161
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• 1996

본 논문에서는 가압열충격의 파괴역학적 해석에 필요한 이론을 조사하였고 원자로용기의 구조건전성을 평가하기 위하여 해석과정을 전산화하였다. 우선 사고 transient에 대하여 원자로용기내의 압력과 주입되는 냉각재의 온도변화가 주어지면 이들로 부터 시간에 따른 용기에서의 온도와 응력분포를 구하고, 중성자 조사량과 용기 재질의 화학성분으로 부터 기준무연성천이온도의 분포가 구해지며 이로부터 파괴인성치 K/sub IA/와 K/sub IC/의 분포가 얻어진다. 또한 응력분포로 부터 균열의 크기 및 형상에 따라 응력확대계수 K/sub I/이 구해지므로 이를 K/sub IA/및 K/sub IC/와 비교함으로써 균열의 성장거동을 예측할 수 있다. 지금까지 보고된 가압열충격을 유발할 수 있는 대표적인 사고 transient가 국내 발전소에 발생할 경우를 가정하여 해석을 수행하였고 그 결과에 대하여 검토하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.667-670
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• 2001

For major structural components periodic inspections and integrity assessments are needed for the safety. However, many flaws are undetectable because sampling inspection is carried out during in-service inspection. Probabilistic integrity assessment is applied to take into consideration of uncertainty and variance of input parameters arise due to material properties and undetectable cracks. This paper describes a Probabilistic Fracture Mechanics(PEM) analysis based on the Monte Carlo(MC) algorithms. Taking a number of sampling data of probabilistic variables such as fracture toughness value, crack depth and aspect ratio of an initial surface crack, a MC simulation of failure judgement of samples is performed. For the verification of this analysis, a comparison study of th PFM analysis using a commercial code, mathematical method is carried out and a good agreement was observed between those results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.155-160
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• 2001

This paper describes a probabilistic fracture mechanics (PFM) analysis based on Monte Carlo (MC) simulation. In the analysis of CANDU pressure tube, it is necessary to perform the PFM analyses based on statistical consideration of flaw generation time. A depth and an aspect ratio of initial semi-elliptical surface crack, a fracture toughness value, delayed hydride cracking (DHC) velocity, and flaw generation time are assumed to be probabilistic variables. In all the analyses, degradation of fracture toughness due to neutron irradiation is considered. Also, the failure criteria considered are plastic collapse, unstable fracture and crack penetration. For the crack growth by DHC, the failure probability was evaluated in due consideration of flaw generation time.